1. Field of the Invention
The present invention relates to the field of semiconductor devices and, more particularly, to an integrated circuit layout and a semiconductor device manufactured using the same.
2. Description of the Related Art
Recently, the design rules of semiconductor devices have been dramatically decreased nearly to the resolution limit of photolithography light sources. One of the problems resulting from the decreased design rules is that specific portion of photoresist patterns may be significantly different from that of corresponding photo mask patterns in both shape and size thereof. For example, the width of a portion of bar type photoresist patterns may be unintentionally narrowed or widened. This phenomenon results from a proximity effect, which is well known in the industry. optical proximity correction (OPC) has been widely used to solve the problem by partially changing the shape and the size of photo mask patterns, thereby compensating the proximity effect.
FIG. 1 is a schematic plan view illustrating a portion of a cell array of a conventional NAND type non-volatile memory device. Referring to FIG. 1, the cell array comprises a plurality of blocks 4 defined in a substrate (not shown). The blocks 4 are preferably arranged repeatedly and symmetrically throughout the cell array. Each of the blocks 4 comprises a plurality of gate patterns formed on the substrate. The gate patterns include selection lines SL and word lines WL. Each of the blocks includes a pair of selection lines SL and a plurality of word lines WL disposed between the pair of selection lines SL.
It is well known that the resolution limit (R) of photolithography technology is inversely proportional to a numerical aperture (NA) of a lens of photo equipment, while it is proportional to a wavelength (λ) of a photolithography light source and a process variable (k). This means that using a light source having a short wavelength may favorably decrease the resolution limit. Usually, due to the small size of word lines and bit lines of a non-volatile memory device, a deep ultraviolet light source is used as a light source for forming photoresist patterns thereof. One example of the deep ultraviolet light source is KrF, the wavelength of which is as short as 248 nanometers (nm). Meanwhile, especially when the size of a pattern is less than half of a wavelength of a light source, the proximity effect becomes serious dramatically. In case of a KrF light source, when the intended size of a pattern is 120 nm or less, the shape and size of a portion of a photoresist pattern may be seriously different from those of a layout pattern of a photo mask.
Each of the blocks 4 has a source line pattern 8 and bit line contact patterns 10 in common with neighboring blocks 4. In other words, at the interfaces between each pair of adjacent blocks 4, either the source line pattern 8 or the bit line contact patterns 10 are formed. The source line patterns 8 and the bit line contact patterns 10 are located between each pair of adjacent selection lines SL. As shown in FIG. 1, the distance d2 between each pair of adjacent selection lines SL is usually designed to be greater than the distance d1 between each pair of adjacent gate patterns of each of the blocks 4, thereby readily accommodating either the source line pattern 8 or the bit line contact patterns 10.
Each of the gate patterns has a first end, a second end and a middle part between the first and second ends. A gate contact pattern 6 is coupled to each of the second end, while each of the first ends is not coupled to any contact pattern. The width of the middle parts of the gate patterns is designed as narrow as a minimum feature size according to a design rule. As shown in FIG. 1, however, the second end of each of the gate patterns is wider than the middle part to accommodate the gate contact pattern 6. The size of the second end is usually two times or more of the minimum feature size.
It is also well known that the proximity effect has pattern dependency. That is to say, the influence of the proximity effect varies portion to portion of the same patterns. In case of the cell array of FIG. 1, the first ends of the gate patterns, at which the contact pattern 6 is not formed, is more seriously influenced by the proximity effect than the other portion of the patterns. As a result of the strong influence of the proximity effect thereon, the first ends of the gate patterns may have a lifting problem, which will be described in detail in conjunction with FIGS. 2 and 3.
FIG. 2 is a plan view illustrating a photoresist patterns for forming the gate patterns of FIG. 1. FIG. 2 is an enlarged plan view corresponding to a portion of the gate patterns around the first ends designated by reference numeral 20 in FIG. 1. FIG. 3 is a cross-sectional view of the photoresist patterns taken along line I–I′ of FIG. 2.
Referring to FIG. 2, the photoresist patterns include word line photoresist patterns WL′ and selection line photoresist patterns SL′. The word line photoresist patterns WL′ are for forming the word lines WL, and the selection line photoresist patterns SL′ are for forming the selection lines SL. The distance between each pair of adjacent selection line photoresist patterns SL′ at the interface between two adjacent blocks is designated by reference L1, and the distance between each pair of adjacent photoresist patterns within each of the blocks is designated by reference L2. As shown in the drawings, the distance L1 is greater than the distance L2 to accommodate either the source line pattern 8 or the bit line contact patterns 10 as described earlier. As indicated by reference numeral 21 in FIG. 2, the photoresist patterns at the first ends may be significantly narrowed by the proximity effect, and the photoresist patterns may be partially lifted from a substrate 23 as indicated by reference numeral 24 in FIG. 3. The partial lifting may induce weak adhesion between the photoresist patterns and the substrate at the first ends.
Another problem at the first ends is a pattern shifting. That is to say, at the interface between adjacent pair of block n and block n-1, a portion of the selection line photoresist patterns SL′ may be undesirably shifted from the originally intended position as indicated by reference numeral 22 in FIG. 2. The pattern-shifting problem results from the above-mentioned weak adhesion as well as a force 26 induced vertically to the selection line photoresist patterns SL′. The vertical force 26 results from a development process of photolithography for forming the photoresist patterns. In other words, during the development process, there are flows 28a, 28b of developing chemicals along spaces between each pair of the photoresist patterns. Reference numeral 28a indicates the flows between the each pair of adjacent selection line photoresist patterns SL′, and reference numeral 28b indicates the flows between the each pair of adjacent photoresist patterns within each of the blocks. Due to the difference between the distance L1 and the distance L2, the velocity of the flows 28a is different from that of the flows 28b, thereby generating the vertical force 26.